The use of prepared mixes and batters has greatly simplified the task of preparing baked goods, particularly cakes which contain flour, sugar, shortening, leavening agents, and other minor ingredients. To prepare the mixes for consumption, aqueous ingredients such as water, milk, eggs, and the like are added to the mix and stirred to form a homogeneous batter. This batter is then baked to produce the final product. The use of such mixes avoids the problem of assembling the various ingredients required, measuring the desired quantities, and mixing them in specified proportions. It is also possible to assemble the dry mix components and the liquid components prior to delivery to the consumer, to further simplify the task of preparing baked goods.
When the culinary mixes designed for baking in a conventional oven by radiant heat are baked in a microwave oven, the resulting cakes are often unacceptable.
For example, during the development of the present invention, a shelf life related problem called crowning was observed. Crowning is defined as a deficiency in the symmetry of the final microwave baked cake where the top center (after inversion and removal from the pan) of the cake is elevated versus the sides as in FIG. 3A. Often this elevated region has a lip on one or more sides creating a very unacceptable appearance. It is to be noted that the top of the finished cake was next to the bottom of the microwave cake pan prior to inversion after the bake.
After considerable experimentation it was unexpectedly discovered that the leavening agents had a significant effect on the crowning problem. Leavening agent ratios, types, and levels needed to be adjusted away from those used in conventionally prepared systems. By adjusting the type and amounts of the leavening agents used, crowning during the shelf life of the microwave cake mixes was reduced, and in many cases, eliminated.
Crowning also occurs in products made from leavened batters that have been processed by mixing or pumping. In this case, it was discovered that crowning was caused by the loss of leavening during processing. After considering the effects of shelf life and processing on crowning, it was determined that gas evolution in the batter just prior to microwave preparation was most important. A test quantitating the amount of gas evolved from 100 grams of batter held at 50.degree. C. for 5 minutes was developed and shown to correlate with an objective measurement of crowning specifically, but also cake symmetry in general (see FIGS. 1 and 6).
Since the crowning problem is not prevalent in conventional cake systems, the cause of this difference was the subject of study.
In conventional ovens, the process of cooking to the center of food masses by conduction and convection requires a temperature gradient, wherein surface temperatures are usually much higher than the final cooked temperature of the food. For example, a gas-fired oven may be maintained at 300.degree. F. to 400.degree. F. to produce a meat roast with an internal temperature of 140.degree. F. In microwave cooking, on the other hand, the ambient temperature in the cooking space is approximately room temperature, and any rise in temperature is very small. The energy of the microwaves is immediately absorbed within the food mass being cooked, and the resulting increase in thermal energy in the food depends on an interaction between the microwave energy and the components of which the food is composed. This interaction can occur throughout the food mass, rapidly produces heat, and results in rapid cooking.
When cake batter is baked in a microwave oven, the microwave energy is unevenly delivered to the fluid batter. The edge of a microwave cake batter is irradiated from three directions, edge, top, and bottom, while the center of the microwave cake batter is irradiated primarily from only two directions. Consequently, heating is more rapid on the edge than in the center. Due to convective heat flow, while the batter is fluid, it rises on the edge and falls in the center. Similarly, because of the uneven heating, the edges reach the temperatures required to set the structure earlier in the baking process than the center. The phenomenon of starch gelatinization is generally considered responsible for setting the structure of a cake (cf. R. C. Hoseney, Principles of Cereal Science and Technology, A.A.C.C. Inc., page 272, 1986), although coagulation of the protein has been implicated as well (cf. Mizukoshi et al., Cereal Chemistry 56, (4), page 305, 1979; and Cereal Chemistry 57, page 352, 1980).
It was discovered that gas evolution affects the symmetry of a cake layer baked by microwaves. Symmetry is measured by measuring the final cake layer thickness in the center and at two opposite edges. The symmetry value is determined by obtaining the sum of the edge measurements and subtracting this from twice the center measurement. Generally, highly leavened batters have high viscosities. Where the batter is poorly leavened, the center of the cake is very fluid in the final stages of the microwave bake, and the downward flow of batter results in the batter flowing under the previously set edge, causing a positive symmetry known as crowning, shown in FIG. 3 A. Optimally leavened batter yields perfect symmetry as shown in FIG. 3B. Overly leavened batter yields negative symmetry (FIG. 3C). Although the overly leavened microwave baking batters have high central viscosity, the center sets with an enlarged cell structure that collapses upon cooling.
Another phenomenon contributing to the symmetry of a microwave cake is the final moisture content of localized areas within the cake. It has been observed that overdone areas, i.e., low moisture areas, within the cake contract. This may be due to contraction of the starch gel that has developed in the cake during microwave cooking. In general, the edge areas are overdone because these areas receive radiation from the sides as well as the top and bottom.
In a highly leavened system, the edge areas evolve large amounts of gas which would tend to lower the relative dielectric constant and relative dielectric loss factor. The dielectric properties and the thickness of a uniform layer are believed to govern the heating rate of the layer. A more detailed discussion of this is found in U.S. patent application Ser. No. 903,007 and the CIP thereof, Ser. No. 85,125 filed Aug. 13, 1987, by Atwell et al. and entitled Microwave Food Product and Method, the disclosures of which are incorporated herein by reference. In general, lower values for the dielectric parameters yield lower heating rates. Thus, a highly leavened system should heat more slowly than a less leavened system. Slower baking translates to higher final moisture and less contraction, particularly in the highly irradiated edge areas. Less contraction around the edges tends to yield more negative symmetries and reduces the "crowning" phenomenon.
Roudebush et al., in U.S. Pat. No. 4,396,635, disclose a microwave cake mix wherein the leavening level is 1-5%, about 1.3% sodium bicarbonate and 1.7% acidulants. This level of leavening is said to provide the best height and texture.
Seward et al., in U.S. Pat. No. 4,419,377, disclose that in microwave cake mixes there is ideally a balance between fast and slow acting acidulants in a leavening system, but no reference is made to symmetry of the baked layers.
Blake et al., in U.S. Pat. No. 4,515,824, disclose a cake mix wherein the leavening agents range from 0.3 to 10%, but there is no reference to symmetry of the layers.